1. Field of the Invention
The present invention relates to a magnetic recording medium manufacturing method in which a magnetic layer is formed by applying and drying a magnetic paint.
2. Description of the Related Art
Conventionally, magnetic recording media such as magnetic tapes referred to as LTO (Linear Tape Open, Registered Trade Mark) and DLT (Digital Linear Tape, Registered Trade Mark) are improved in recording density by means of reducing the size of magnetic particles constituting a magnetic layer or other method. Also, in the future, further improvement in the recording density is desired.
Here, a problem arises in that, for example, the influence of self demagnetization due to a demagnetizing field increases as the recording density increases. However, the influence of self demagnetization due to the demagnetizing field can be suppressed by reducing the thickness of a magnetic layer. Therefore, as the recording density increases, the thickness of a magnetic layer is often reduced.
In order to facilitate the understanding of the present invention, a brief description will be given of an example of a method of forming a magnetic layer of a magnetic tape.
First, while a nonmagnetic film-shaped support and a nonmagnetic underlayer formed thereon are fed along the plane direction thereof, a nozzle is brought into proximity to the surface of the support to discharge a magnetic paint containing magnetic particles and the like onto the underlayer from the end of the nozzle. Hence, the magnetic paint is applied to the surface of the underlayer to a predetermined wet film thickness. Subsequently, solvent components of the applied magnetic paint are volatilized for drying the magnetic paint to thereby form a magnetic layer having a predetermined dry film thickness.
The thickness of the magnetic layer may be reduced by applying the magnetic paint to a small wet film thickness. However, when the magnetic paint is applied to an excessively small thickness, a problem arises in that defects such as application defects of the magnetic paint are likely to occur.
Therefore, conventionally, the occurrence of defects such as application defects of magnetic paint has been suppressed by applying a magnetic paint to the surface of an underlayer to a sufficiently large wet film thickness of a certain value or larger. In addition to this, the thickness of a magnetic layer has been reduced by reducing the solid concentration NV (non-volatile) of the magnetic paint (see, for example, Japanese Patent Laid-Open Publication No. 2005-108313).
In the above case, a magnetic paint is applied to the surface of a support to a sufficiently large wet film thickness of a certain value or larger. However, even in this case, when a thin magnetic layer having a dry film thickness of, for example, 60 nm or less is formed, fine stripe-like defects (many stripes of several μm in width and several tens of μm in length) may be formed on the surface of the magnetic layer. These defects increase the surface roughness of the magnetic layer surface and thus may cause problems such as an increase in error rate.